The vacuolar proton-translocating ATPase, or V-ATPase, is a multi-subunit complex that uses energy from ATP hydrolysis to transport protons across cellular membranes. In most eukaryotes, V-ATPases reside solely in membranes of the endocytic network, where they serve to acidify endosomes, lysosomes, the trans-Golgi, and other vacuolar compartments. However, some specialized cell types, including kidney epithelia, osteoclasts, macrophages, and neurons, express the V-ATPase at high levels and in specialized subcellular compartments, where the enzyme is critical for such diverse functions as urinary acidification, bone resorption, regulation of intracellular pH, and regulated vesicular uptake of neurotransmitters. The variety of functions performed by V-ATPases among mammalian cells is attributable to expression of multiple subunit isoforms, differences in overall expression levels, and the capacity for regulated targeting to specialized membrane compartments. Inappropriate expression of V-ATPase in humans has been shown to lead to serious disease states, including renal tubular acidosis, deafness, and osteopetrosis. The genetic controls that regulate V-ATPase expression must be varied and diverse to meet the specific proton-transport needs of many specialized cell types, as well as its constitutive role in the endocytic network. These include both transcriptional and post-transcriptonal mechansims, as well as intracellular targeting of both V-ATPase mRNA and proteins. The long-term goal of this project is to understand the mechanisms by which V-ATPases are expressed at appropriate levels and in appropriate membrane compartments. To this end, the specific aims are directed toward (1) examining mechanisms by which V-ATPase mRNA stability is regulated in proton-secreting cells such as macrophages and kidney epithelia; (2) examining determinants within V-ATPase mRNAs that mediate intracellular trafficking in specialized cell types; and (3) defining genetic elements that control expression of a uniquely regulated V-ATPase subunit involved in intracellular trafficking. These aims will be achieved through experiments in which V-ATPase mRNAs are genetically manipulated in cell culture models; the effects of these manipulations of V-ATPase expression and cell function will be determined.